Why Grid Synchronous Inertia Helps to Keep the Lights On

By Gary Preece, Highview Power’s Chief Market Development Officer.

In November 2022 the National Grid warned that the UK could face a winter of power cuts due to the expected rise in energy demand coupled with depleted gas storage supplies. The ‘rolling blackouts’ did not materialise. However, the spotlight turned once again onto the ability of our infrastructure to optimise renewable energy when in February two coal-fired power plants were put on standby in case additional energy sources were needed when temperatures fell.

Apart from during an occasional extreme weather event, such as Storm Frank in 2015 and 2016, the UK has been able to rely on secure access to electricity for decades. The threat to our energy security from geopolitical events and rising costs in the past few months, however, has put National Grid Plc under pressure to reinforce the stability of the network. A key part of this will be energy storage.

Outages usually occur due to a systemic failure to maintain grid frequency because of a deficiency in system inertia. Frequency and inertia are essential to the successful operation of the electricity network and to enabling the UK to reach its goal of making renewables a baseload power source.

System inertia resists changes in grid frequency caused by the shifts in demand and generation. Traditionally, this has been accomplished by the rotating masses of turbines and rotors electromagnetically coupled to the system (synchronous) – a valuable by-product of conventional generation. Because it is challenging to stop large rotating masses once they are spinning, they therefore have high inertia. Electromagnetically coupled equipment also delivers short circuit power.

Today’s modern power grid is significantly more reliant on renewable energy supplies, but sources such as wind and solar have almost no inertia. Apart from pumped hydro, renewables do not include the spinning reserve that is electromagnetically coupled to the system. While thousands of solar arrays and a growing number of wind farms connect to the grid to provide clean energy, they also contribute to an expanding vacuum of inertia, making it harder to maintain consistent frequency. There is also diminishing short circuit power.

Solving this challenge requires a method of creating synchronous inertia within the grid from renewables. The National Grid and UK Government is investing in a stable system that enables wind, solar and lithium-ion (inverter based systems) to perform in a way that allows frequency to be consistent.

Highview Power’s long duration energy storage technology has the answer. Our system includes rotating masses that can be electromagnetically coupled to the grid to provide inertia, and to contribute to short circuit power, having the scale and characteristics required for “Black Grid Restoration”.

The instantly available inertia of rotating masses provided by our liquid air energy storage system is not to be confused with “synthetic inertia” – which can be provided by power electronics or batteries, for example – which is necessarily delayed by measurement (approx. 80 milliseconds), by which time frequency could have deviated sufficiently to trigger protection (on RoCoF (rate of change of frequency)).

With it’s integrated “Stability Island”, the Highview Power system maintains grid synchronisation in both charging or discharging phase, as it uses both a turbine and synchronous generator (discharging) and a compressor and synchronous motor (charging). The Stability Island, with a clutch and flywheel, further increases capabilities.

The benefit of a synchronous system is that it provides the grid with more stable frequency, reduces the threat of demand disconnections and allows energy storage to be optimised in support of a Net Zero energy future.

About the Author

Gary Preece is a leading Chartered Electrical Engineer with over 30 years experience in the power industry. He has delivered many power system designs including taking the lead for power system on the Type 26 Global Combat Ship, a class of frigate built for the Royal Navy that is now in production with BAE Systems.

Prior to joining Highview, he was the Group Power System Lead at Drax Power Ltd where he led on numerous key programmes.  At Highview, Gary is responsible for the techno commercial analysis and revenue assumptions that underpin the deployment of the business’s LAES System.